1. Field of the Invention
The present invention relates to a developing device that is applicable to, for instance, electrophotographic copying machines.
2. Description of the Related Art
A developing device of this type, equipped with a developing magnet roller and upper and lower mixers, circulates developer along upper and lower conveying paths by rotating the upper and lower mixers and develops images by supplying developer to the developing magnet roller from a developer accumulating portion via the upper conveying path.
Further, after developing images, residual developer remaining on the developing magnet roller is recovered and conveyed along the lower conveying path.
By the way, the developer accumulating portion and the lower conveying path are communicated with each other and developer tends to leak from the developer accumulating portion to the lower conveying path. Leakage (flow) of developer to the lower conveying path is prevented because developer is retained by the magnetic force of a conveying pole located close to the developer accumulating portion of the developing magnet roller.
However, in conventional developing devices, developer is retained by the magnetic force of the conveying pole and if the magnetic force of the conveying pole drops, the developer leaks (flows) from the developer accumulating portion to the lower conveying path and the circulation of developer is unbalanced. That is, there was such a defect that developer in the upper conveying path decreases, amount of developer supplied to the developing magnet roller via the developer accumulating portion drops and in the worst case, developer may not be supplied.
Further, when the magnetic force of the conveying pole is too high, used developer is drawn in the developer accumulating portion from the lower conveying path and an image density is apt to drop.